Electron precipitation zones around major ground-based VLF signal sources

The spatial distribution of electron precipitation induced by VLF signals from ground-based transmitters is determined by using a test particle computer model of the gyroresonant wave-particle interaction (Inan et al., 1982). The results are presented as contours of energy flux on a map of the region around each transmitter. It is shown that the size of the precipitation zones is a strong function of the geographic location of the transmitter, as well as its radiated power and operating frequency. In general, the precipitation zones are much wider in longitude than in latitude and are oriented along lines of constant geomagnetic latitude. Assuming backscatter and/or wave echoing, precipitation zones around the points that are magnetically conjugate to the sources are also estimated. The results presented can be used to interpret satellite- or ground-based measurements of the precipitation induced by ground-based VLF transmitters.